@hackage llvm-ffi21.0.0.2

Installation

Installation cannot be done fully automatically. It would require Cabal code that is bound to certain Cabal versions and is prone to fail. We give several non-automatic ways that also allow you to choose a particular LLVM version.

First possibility is to point Cabal to the LLVM installation directories manually. It is recommended to add options to your global .cabal/config:

extra-include-dirs: /usr/lib/llvm-21/include
extra-lib-dirs: /usr/lib/llvm-21/lib

This works for both v1-build and v2-build. The shown paths work for Debian and Ubuntu using the LLVM repositories at https://apt.llvm.org/. You can obtain them with

llvm-config-21 --includedir --libdir

You can choose specific LLVM versions per project. For v1-builds it works like so:

cabal install -fllvm1300 --extra-include-dirs=$(llvm-config-13 --includedir) --extra-lib-dirs=$(llvm-config-13 --libdir) yourpackage

For Nix-style build you must add some options to the cabal.project.local file of your LLVM-related project:

package llvm-ffi
  flags: +llvm1300
  extra-include-dirs: /usr/lib/llvm-13/include
  extra-lib-dirs: /usr/lib/llvm-13/lib

Alternatively, you may set environment variables globally or locally:

export CPATH=/usr/lib/llvm-21/include:$CPATH
export C_INCLUDE_PATH=/usr/lib/llvm-21/include:$C_INCLUDE_PATH
export LD_LIBRARY_PATH=/usr/lib/llvm-21/lib:$LD_LIBRARY_PATH

You can install and make LLVM library available in an elegant way using Nix:

nix-shell -p llvmPackages_21.libllvm

Though, for compatibility of GHC with LLVM and GLIBC you will need to use more packages from Nix and you better use a shell.nix file for bundling those:

let
  pkgs = import <nixpkgs> {};
  llvmPkgs = pkgs.llvmPackages_21.libllvm;
in
pkgs.mkShell {
  nativeBuildInputs = (with pkgs; [
    gnumake
    pkg-config
    ghc
    cabal-install
    llvmPkgs
  ]);
  CPATH="${llvmPkgs.dev}/include";
  C_INCLUDE_PATH="${llvmPkgs.dev}/include";
  LD_LIBRARY_PATH="${llvmPkgs.lib}/lib";
}

The second way uses pkg-config. You can store above paths permanently in a pkg-config file like llvm.pc. The optimal way would be if LLVM installations or GNU/Linux distributions would contain such a file, but they don't. Instead, you may generate it using the llvm-pkg-config package or write one manually. Then you run

cabal install -fpkgConfig

We ship a pkg-config.nix file. If you import this into your Nix expression, Nix will prepare and install a llvm.pc file for you.

Known issues

Warning for inplace builds: Re-configuring the package using, say -fllvm1600, and re-buildung it might result in corrupt code. You must make sure that the stuff in cbits is re-compiled. Cabal or GHC may forget about that. You are safe if you run cabal clean.

Caution: Surprises are ahead if you have configured paths for LLVM version X in .cabal/config and try to build llvm-ffi for a different LLVM version Y by adding custom include and library paths to cabal.project. Counterintuitively, global search paths take higher precedence than local ones.

We now depend on libLLVM.so, not on libLLVM-X.so anymore. This is for consistency with the include files, where there are no include file names including version numbers. In former versions of this binding package we depend on generic LLVM/Core.h but specific libLLVM-X.so. This meant, that the include files configured in .cabal/config were mixed with the library configured in cabal.project. This lead to ugly, hard to debug crashes.